linoleic-acid and 2-amino-3-methylimidazo(4-5-f)quinoline

The cooking of meat and fish produces heterocyclic amine mutagens, including 2-amino-1-methyl-6-phenylimidazo[4,5b]pyridine (PhIP) and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). Chronic administration of PhIP or IQ to the F344 rat induces tumors at several sites, including adenocarcinomas of the colon, and short-term treatment leads to the formation of colonic aberrant crypt foci (ACF). We have used these end-points to identify potential chemopreventive agents that might be effective against heterocyclic amine colon carcinogens. Typically, IQ or PhIP were administered to groups of 10-15 rats by oral gavage on alternating days in weeks 3 and 4, and ACF were scored after 8, 12, or 16 weeks or tumors were detected at 52 weeks. To distinguish between 'blocking' and 'suppressing' agents, potential inhibitors were administered during the initiation or post-initiation phases, respectively, and subsequent studies focused on the inhibitory mechanisms. Among the most effective inhibitors identified to date, and their major mechanisms, were the following: chlorophyllin (molecular complex formation); indole-3-carbinol (inhibition and induction of cytochromes P450 and phase II enzymes); green and black tea catechins (induction of UDP-glucuronosyl transferase, inhibition of NADPH-cytochrome P450 reductase, scavenging of reactive intermediates); and conjugated linoleic acids (inhibition of cytochrome P450 and prostaglandin H synthase).

Topics: Animals; Anticarcinogenic Agents; Carcinogens; Catechin; Chlorophyllides; Colon; Colonic Neoplasms; Drug Antagonism; Imidazoles; Indoles; Linoleic Acid; Precancerous Conditions; Quinolines; Rats; Rats, Inbred F344

Meats cooked at high temperatures contain mutagenic heterocyclic amines such as 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). In female Fischer 344 rats, IQ is a multiorgan carcinogen, whereas PhIP induces mammary adenocarcinomas. For IQ and PhIP, N-hydroxylation, catalyzed by microsomal cytochrome P-450 1A1 and/or 1A2, and then esterification, especially O-acetylation, are the principal steps leading to DNA adduct formation. Conjugated linoleic acid (CLA) is a mixture of conjugated linoleic acid isomers found in various meat and dairy products. We have examined the effect of dietary CLA on DNA adduct formation by PhIP and IQ in female Fischer 344 rats. Four-week-old animals were maintained on AIN-76A diet without or with CLA (4% wt/wt) and treated with IQ or PhIP (50 mg/kg by gavage) after two weeks. Animals were killed (4/group) one, four, and eight days later. DNA isolated from mammary epithelial cells, liver, colon, and white blood cells was analyzed for carcinogen-DNA adducts by 32P-postlabeling assays. On Day 1, dietary CLA significantly inhibited adduct formation (82.0%) in mammary epithelial cells in IQ--but not in PhIP-treated rats. In the colon, dietary CLA significantly inhibited PhIP-DNA adduct formation (18.7%) on Day 8 but increased IQ-DNA adduct formation (30.5%) on Day 8. Dietary CLA had no effect on adduct levels in liver or white blood cells. Calf thymus DNA was incubated with N-hydroxy-PhIP or -IQ in the presence of acetyl-CoA. Enzymatic activation was catalyzed by liver or mammary cytosol. A two-week pretreatment with 2% (wt/wt) dietary CLA had no effect on O-acetyltransferase-catalyzed IQ- or PhIP-DNA adduct formation. It is concluded, under certain conditions, that dietary CLA can lower IQ- and PhIP-DNA adduct formation. Overall, however, the major mode of action of CLA is probably by a mechanism other than the inhibition of the N-hydroxylation and subsequent O-acetylation of PhIP or IQ.

Topics: Acetyl-CoA C-Acetyltransferase; Animals; Anticarcinogenic Agents; Carcinogens; Dietary Fats, Unsaturated; DNA Adducts; Female; Imidazoles; Linoleic Acid; Liver; Mammary Glands, Animal; Mammary Neoplasms, Experimental; Quinolines; Rats; Rats, Inbred F344

The dietary mutagens 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) are carcinogenic in rodents. In F344 rats PhIP induces mammary tumors in females and colon tumors in males, while IQ induces tumors principally in the liver, Zymbal gland and intestines. In CDF1 mice, IQ induces liver, lung and forestomach tumors. We have evaluated the dynamics of formation, removal and inhibition of PhIP- and IQ-DNA adducts in these rodents. After bolus doses (50 mg/kg, by gavage) of IQ or PhIP, both IQ- and PhIP-DNA adducts were removed rapidly from both target and nontarget organs, while after 3-4 weeks of feeding IQ or PhIP (0.01-0.04%) adduct removal was much slower. Gavaging of male F344 rats with PhIP (0.1-1000 micrograms/kg/day) for 23 days resulted in accumulation of PhIP-DNA adducts in various organs, but adducts were detectable only at 100 or 1000 micrograms/kg/day. Urinary excretion of unchanged PhIP was a constant proportion (1.6-2.1%) of the daily dose over the entire dose range and was independent of duration of exposure. When weanling female F344 rats were exposed to dietary PhIP (0.01-0.04%) for 1-4 weeks, the presence of either conjugated linoleic acid (CLA; 0.1-1.0%) or indole-3-carbinol (13C; 0.1%) in the diet inhibited PhIP-DNA adduct formation (58-99%) in various organs, including the mammary gland and the colon. Similarly, the inclusion of 0.075% 4-ipomeanol (IPO) in the diet of male CDF1 mice exposed for 3 weeks to dietary IQ (0.01%) resulted in inhibition of IQ-DNA adduct formation (30-59%) in the target organs (liver, lungs, stomach) but not in a number of other organs. It is concluded that (1) the rate of PhIP- and IQ-DNA adduct removal depends on the dose and frequency of administration, (2) urinary PhIP may be a good biomarker of recent PhIP exposure and (3) CLA, I3C and IPO are potential chemopreventive agents against PhIP- or IQ-induced tumors in rodents.

Topics: Amines; Animals; Antimutagenic Agents; Carcinogens; Diet; DNA Adducts; DNA Repair; Female; Gastric Mucosa; Heterocyclic Compounds; Imidazoles; Indoles; Linoleic Acid; Linoleic Acids; Liver; Male; Mammary Glands, Animal; Mice; Quinolines; Rats; Rats, Inbred F344; Terpenes; Tissue Distribution

Grilled ground beef contains a number of heterocyclic amine carcinogens, such as 2-amino-3-methylimidazo[4,5-f] quinoline (IQ), as well as anticarcinogenic conjugated linoleic acids (CLA). In the present study, CLA was administered to male F344 rats by gavage on alternating days in weeks 1-4, while IQ was given by gavage every other day in weeks 3 and 4 (100 mg/kg body wt). Rats were killed 6 h after the final carcinogen dose 16 in order to score colonic aberrant crypt foci (ACF). In the ACF study, CLA had no effect on the size of the foci, but inhibited significantly (P < 0.05) the number of ACF/colon, from 4.3 +/- 2.4 in controls to 1.1 +/- 1.3 in CLA-treated rats (mean +/- SD, n = 10). Rats given CLA also had significantly lower IQ-DNA adducts in the colon as determined by 32P-postlabeling analysis; relative adduct labeling levels (RAL x 10(7) for the major adduct were 9.13 +/- 2.6 in controls versus 5.42 +/- 1.8 in CLA-treated animals (P < 0.05). Mechanism studies indicated that CLA and other fatty acids interact with certain heterocyclic amines in a manner consistent with substrate-ligand binding. However, no such interaction occurred with IQ, and CLA failed to inhibit significantly the mutagenicity of N-hydroxy-IQ in the Salmonella assay. Liver microsomes from CLA-treated rats exhibited lower activities for dealkylation of 7-ethoxyresorufin and methoxyresorufin and activated IQ to DNA binding species less effectively than microsomes from control animals. Direct addition of CLA to the in vitro incubation inhibited IQ-DNA binding and was associated with increased recovery of unmetabolized parent compound. In the Salmonella assay, CLA inhibited the mutagenic activity of IQ in the presence of S9 or ram seminal vesicle microsomes. Collectively, these results support a mechanism involving inhibition of carcinogen activation by CLA, as opposed to direct interaction with the procarcinogen, scavenging of electrophiles or selective induction of phase I detoxification pathways.

Topics: Animals; Anticarcinogenic Agents; Antimutagenic Agents; Carcinogens; Colonic Neoplasms; DNA Adducts; Enzyme Induction; Linoleic Acid; Linoleic Acids; Male; NADH, NADPH Oxidoreductases; NADPH-Ferrihemoprotein Reductase; Quinolines; Rats; Rats, Inbred F344; Substrate Specificity

Grilled ground beef contains a number of carcinogens, including aminoimidazoazaarenes, such as 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), as well as anticarcinogenic substances, such as heat-generated derivatives of linoleic acid (CLA). In the present study, CLA was administered by gavage every other day to young adult CDF1 mice for a period of 45 days (50 microliters/48 hr for days 1-24 and 100 microliters/48 hr for days 25-45), using trioctanoin as a control. On day 46 all animals received a single oral dose (50 mg/kg) of IQ and tissues were collected 24 hr later. Tissue DNA was purified and analysed for IQ-DNA adducts by 32P-postlabelling assays. Compared with controls, CLA treatment caused a 43.1 and 31.8% inhibition of adduct formation in the livers of male and female mice, respectively. In the lung and large intestine CLA had a 74.2 and 39.4% inhibitory effect, respectively, in the female only, whereas there was no effect in the stomach or small intestine of either sex. In the kidneys of females, CLA treatment inhibited IQ-DNA adduct formation almost completely (95.2%), whereas in the kidneys of males CLA had no effect. It is concluded that CLA inhibits IQ-DNA adduct formation in certain IQ target organs (liver and lung) and non-target organs (large intestine, kidney), but is inactive in other target organs (stomach) and non-target organs (small intestine) of the CDF1 mouse.

Topics: Administration, Oral; Animals; Antimutagenic Agents; Autoradiography; DNA; Female; Hot Temperature; Linoleic Acid; Linoleic Acids; Male; Mice; Mutagens; Quinolines